Joining seller forums is a great way to get fabulous information on just about everything.
Also some (always look at posting rules!) allow promoting your sites, stores, blogs & more. Even if they don't allow any promoting... most allow signatures with your site address.
So here are a few that have been "a bucketload" of information & you can make friends at the same time.
The trick to finding forums you are interested in.... simply google your interest & forum or message boards. SAHMs.... WAHMs ... RVers .... Gardening .... Crafters .... pets ... dogs...
If you sell to a "targeted" group.... join in those groups too! And think outside the box.... if you are a travel agent, join some senior's or wedding groups. If you sell bath & body gift items, join "mom groups". You just never know who will be there & want to buy your "stuff". Google picks up those forums & the posts too!